The present invention relates to a self-adhesive silicone rubber composition or, more particularly, to a silicone rubber composition capable of firmly adhering to the surface of various kinds of substrate materials such as metals, glass, ceramics, plastics, fibers, rubbers and the like even without the pre-treatment of the surface with a primer as well as to a silicone rubber-coated fabric web prepared by coating a fabric web with the silicone rubber composition and curing the same.
Silicone rubber compositions in general have surface-releasability more or less so that firm adhesive bonding usually cannot be obtained between a cured silicone rubber composition and the surface of a substrate material, such as metals, glass, ceramics, plastics, fibers and fabric webs, rubbers and the like, on which the silicone rubber composition has been cured. This disadvantage can be solved at least partly by treating the substrate surface with a so-called primer before the substrate surface is contacted with an uncured silicone rubber composition.
On the other hand, silicone rubber-coated fabric webs, i.e. woven cloths, knit cloths and non-woven cloths, are prepared by coating a fabric web with a silicone rubber composition and curing the silicone rubber composition so as to have the silicone rubber composition cured on and firmly adhering to the substrate surface. Such a silicone rubber-coated fabric web is widely used as an electric insulating material, diaphragms, sealing material, material of air bags, tenting sheet, duct hose and the like. Proposals have been made in Japanese Patent Publication No. 42-2687 and Japanese Patent Kokai No. 55-152863 for the use of a silicone rubber-coated fabric web as a material of medical use or clothing use. A problem in these silicone rubber-coated fabric webs is that firm adhesive bonding can hardly be obtained between the cured silicone rubber layer and the surface of the fabrics as the substrate, in particular, when the fabric web is formed from synthetic fibers having polar groups such as amide groups of the formula --CO--NH-- as is the case in nylons, aromatic polyamide fibers and the like.
The treatment with a primer is indeed effective in improving the adhesive bonding between a cured silicone rubber composition and various kinds of substrate surfaces. Practically, however, the primer treatment has several disadvantages as an industrial process even by setting aside the troublesomeness of the molding process which must be preceded by the primer treatment. Since primers are usually used in the form of a solution in an organic solvent, for example, vapor of the organic solvent causes a serious problem of environmental pollution necessitating expensive facilities for ventilation along with an adverse influence on the health of workers. When a strong shearing force is added to the primer-coated substrate surface as in the injection molding, in addition, the primer layer sometimes causes a plastic flow eventually to be removed from the substrate surface leading to an uneven priming effect.
In this regard, so-called self-adhesive silicone rubber compositions have been developed which can be cured into a cured silicone rubber firmly adhering to the substrate surface on which the composition has been cured even by omitting the primer treatment of the substrate surface. Self-adhesive silicone rubber compositions of a class are prepared by admixing a silicone rubber composition with an alkylperoxy silane compound as an adhesiveness-imparting agent including, for example, vinyl tris(tert-butylperoxy) silane, triphenyl tert-butylperoxy silane, trimethyl tert-butylperoxy silane, methyl vinyl di(tert-butylperoxy) silane and the like. Further, it is known that a silicone rubber composition can be imparted with self-adhesiveness by the admixture of a so-called carbon-functional silane coupling agent such as vinyl trimethoxy silane, vinyl triethoxy silane, 3-glycidyloxypropyl trimethoxy silane, 3-methacryloxypropyl trimethoxy silane and the like. It is also known that a benzoate compound having a vinyl-substituted silyl group such as tert-butylperoxy-4-vinyl dimethylsilyl benzoate and the like serves simultaneously as an adhesiveness-imparting agent and as a curing agent since the compound is an organic peroxide.
The above described silicone rubber compositions are not quite satisfactory as a self-adhesive rubber composition. For example, the alkylperoxy silane compounds cannot impart the silicone rubber composition with sufficiently high self-adhesiveness. The silicone rubber composition compounded with a silane coupling agent is also not quite satisfactory in respect of the self-adhesiveness and the durability of adhesive bonding. The benzoate compound is practically not advantageous in respect of the cost for the compound due to the difficulty in the synthetic preparation thereof as well as in respect of the low durability of the adhesive bonding at an elevated temperature between the substrate surface and the cured silicone rubber layer prepared by the admixture of the same.